Apparatus for selective chemical vapor deposition of dielectric, semiconductor and conductive films on semiconductor and metallic substrates

ABSTRACT

An apparatus and method for chemical vapor deposition in which the reactants directed toward a substrate to be provided with one or more films are first subjected to an electric field. The electric field is applied between two electrodes and the reactants become polarized in the field, thus stretching their polarized chemical bonds close to the breaking point. The apparatus also applies voltage pulses between one of the electrodes and the substrate. By adjusting the pulse height, pulse width and pulse repetition rates, the chemical bonds of polarized reactants break to produce free radicals and some ions of the desired elements or compounds. The substrate is kept at a given temperature. The free radicals react to deposit the desired film of high purity on the substrate. The deposition characteristics of the deposited films in terms of isotropic, anisotropic and selective deposition are controlled by the pulse height, width, repetition rates and by other process parameters. Such parameters also control the grain size and orientation of the deposited films. By choosing appropriate reactants other than those for CVD, e.g., for reactive ion etching (RIE), in-situ cleaning prior to CVD, RIE and post CVD etching and treatment of the films can be accomplished. The latter technique is useful for achieving in-situ planarization. To aid the dissociation process for producing the free radicals in ions from the reactants, an axial magnetic field axial to the direction of the applied electric field may also be used.

This is a division of application Ser. No. 07/743,546 filed Aug. 9,1991, now U.S. Pat. No. 5,212,118.

This invention relates to improvements in the formation of semiconductorand industrial/airline components and, more particularly, to apparatusand method for film deposition by chemical vapor techniques.

BACKGROUND OF THE INVENTION

In the conventional fabrication of microelectronic integrated circuits(I.C.'s), a variety of dielectric films (e.g., SiO2, Si3N4),semiconductor films (e.g., epitaxial Si, polycrystalline Si, GaAs) andconductor films (e.g., W, WSi2, TiN) are deposited by chemical vapordeposition (CVD) processes. These CVD processes are well known in thesemiconductor processing field and can be classified into the followingcategories:

Thermal CVD (CVD, LPCVD, APCVD)

In this type of process, thermal energy is used to cause a chemicalreaction to occur and to cause a deposit of the desired film on asubstrate. Examples of the process are as follows: ##STR1##

The temperatures required in the thermal CVD processes are generallyhigher than those required in the plasma enhanced CVD (PECVD) and photoCVD (PHCVD) processes described below. Also, a thermal CVD process tendsto be isotropic because there is no energy in addition to thermal energywhich can give direction to the chemical reaction which occurs. Thiscontributes to the void formation in patterned geometries of smalldimensions (<1 um) and pitches (<2 um) having large aspect ratios (>1).

Some variations of the CVD processes are to carry them out at lowpressures (LPCVD), e.g., 1-10 mTorr, or at atmospheric pressures(APCVD), e.g., 500-760 mTorr. The differences in the LPCVD and APCVDprocesses in terms of the deposition rates and film properties dependupon the reaction chemistry. However, in general, the deposition ratesin a LPCVD process are lower than in an APCVD process because thedensity of the reactants is smaller in the LPCVD process.

Plasma Enhanced CVD (PECVD)

In this type of process, a plasma is generated to create ions, freeradicals and electrons which aid the chemical reaction to occur, usuallyat temperatures lower than those required for thermal CVD, and toproduce the desired film on the substrate. The PECVD process is done atlow pressures (e.g., 1-10 mTorr) which is necessary to create andsustain the plasma. This pressure constraint is one of the disadvantagesof LPCVD because the density of the reactants is less than that inAPCVD, which can result in lower deposition rates in the former.Examples of PECVD process is as follows: ##STR2##

The free radicals generated in the plasma are very reactive, and theirconcentration is much higher than that of the ions. This can lead to gasphase nucleation of the reaction, causing unwanted particulatecontamination in the film. Further, the unwanted species generated inthe plasma as free radicals get incorporated in the film causingdeleterious effects. The reactions occurring in a plasma process arequite complex. They depend on a variety of variables such as r.f. power,frequency, duty cycle, reactants, pressure, temperature and the designof the process chamber and electrodes of the system.

Photon-Induced CVD (PHCVD)

In this process, high-energy and high-intensity photons are used todissociate and excite the reactant species in the gas phase for thechemical reaction to occur at rather low temperatures (e.g., even atroom temperatures). The PHCVD process is done usually at nearatmospheric pressure (e.g., 500-760 mTorr). For efficient transfer ofthe photon energy to the reactants for their excitation, catalyticagents such as mercury vapor are used for some processes. Also, lasersare used for some processes such as direct writing because of theirfrequency tunability and high intensity. However, PHCVD processes havenot yet become production-worthy because of low density and depositionrate of, and contamination in, the deposited films.

Because of the numerous problems associated with conventional CVD asdescribed above, a need exists to provide improvements in CVD. Thepresent invention satisfies this need.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and method forchemical vapor deposition in which the reactants directed toward asubstrate to be provided with one or more films are first subjected toan electric field. The reactants first pass through the electric fieldapplied between two electrodes and the reactants become polarized, thusstretching their polarized chemical bonds close to the breaking point.

The apparatus also includes pulse means which apply a voltage pulsebetween one of the electrodes forming the electric fields and thesubstrate, the latter generally being kept at ground potential. Byadjusting the pulse height, pulse width and pulse repetition rates, thechemical bonds of polarized reactants break to produce free radicals andsome ions of the desired elements or compounds. Relatively large numbersof these free radicals are created without the generation of a plasmawhich also means that the number of electrons produced is very small inthe volume near the substrate which is kept at a given temperature. Thefree radicals react to deposit the desired film of high purity andalmost free from particulate contamination. The ionized species of thereactants are much smaller in number than the free radicals. Due to thesmall number of ions and electrons generated, their deleterious effectsare minimized, and the deposited films are almost free of radiationdamage.

The deposition characteristics of the deposited films in terms ofisotropic, anisotropic and selective deposition are controlled by thepulse height, width, repetition rates and by other process parameters.Such parameters also control the grain size and orientation of thedeposited films. By choosing appropriate reactants other than those forCVD, e.g., for reactive ion etching (RIE), in-situ cleaning prior toCVD, RIE and post CVD etching and treatment of the films can beaccomplished. The latter technique is useful for achieving in-situplanarization.

Selective CVD of a material, for instance, tungsten, on a surface, forexample, AlCu, exposed through vias or trenches in a dielectric film, orvice versa, can be accomplished with the present invention by adjustingthe pulse height, width and repetition rates. The differential inducedcharge on the desired surface causes selective CVD on such surface butnot on the surrounding surfaces. By increasing the pulse height beyondthe value needed for just breaking the chemical bond of the reactant,the energy of the desired element or compound can be increased. Thisfeature of the present invention can provide a better epitaxial growth,for instance, of silicon, at temperatures lower than in the conventionalprocesses mentioned above. Also, surface implantations or coatings canbe achieved on large surfaces whether or not they are planar.

To aid the dissociation process for producing the free radicals from thereactants, an axial magnetic field axial to the direction of the appliedelectric field may also be used.

The primary object of the present invention is to provide an apparatusand method for chemical vapor deposition of dielectric, semiconductorand conductor films on a substrate after a reactant or reactants havepassed through an electric field which stretches the polarized chemicalbonds of the reactants close to the breaking point, following whichelectrical pulses are applied to the electric field to break up thereactants and cause the reactants to produce free radicals and some ionswithout the generation of plasma so that the free radicals react todeposit the desired film of high purity on the substrate with the filmbeing substantially free from particulate contamination and radiationdamage.

Another object of the present invention is to provide an apparatus andmethod of the type described, wherein the deposition and characteristicsof the films in terms of isotropic, anisotropic and the selectivedeposition are controlled by the height, width, repetition rates ofpulses applied to the electrode from which the reactants emerge so as tocontrol the grain size and orientation of the films deposited on thesubstrate.

Other objects of this invention will become apparent as the followingspecification progresses, reference being made to the accompanyingfigure of drawing which shows a schematic view of the apparatus of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrate the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus of the present invention is broadly denoted by the numeral20 and includes a hollow housing 22 defines a process chamber 1 havingan inlet 2 for directing reactants, such as oxygen, silane, othercompounds transported in the vapor phase, or their mixtures as requiredby the CVD processes. The apparatus has a port 17 for viewing and/orphoton induced CVD.

Housing 22 has a lower hollow space 24 which is generally annular and influid communication with and forms a part of chamber 1. Space 24 has anoutlet 3 to be coupled to a vacuum pump (not shown) for exhausting thespace 24 of contaminants or reactants.

Means 16 is provided for mounting a substrate 4 on a heater assembly 13surrounded by space 24. The mounting means 16 positions the substrate 4at a location in space 24 aligned with chamber 1 so that reactantsdirected into chamber 1 will move downwardly and toward and onto theadjacent surface of the substrate after the reactants have passedthrough the electric field as hereinafter described. The entireapparatus can be configured easily such that the substrate surface isvertical, when appropriate modifications for substrate mounting andtransport are made. Such modifications can be made by those conversantin the state of the art. It would further minimize theparticle/contaminant deposition on the surface of the substrate, therebygiving higher quality films.

An upper electrode 6, preferably in the form of a perforated plate, iscoupled to the inner surface of housing 22 and extends across chamber 1.A second electrode 8, preferably a perforated plate, is mounted on theinner surface of housing 22 in chamber 1 near its lower end thereof andspaced below the electrode 6. A voltage source 6A is coupled by a lead6B and a feedthrough device 5 to electrode 6 for supplying voltagethereto. Similarly, a voltage source 8A is coupled by a lead 8B througha feedthrough device 7 to electrode 8 for supplying voltage to electrode8. The voltage difference applied to the electrodes 6 and 8 produce anelectric field whose intensity can be varied as desired. For instance,the voltage applied to electrode 6 can be cathodic and vary from +100 Vto +1000 V while the voltage applied to electrode 8 can vary from a +1 Vto +100 V. In such a case, the polarity of the electrodes would be suchthat electrode 6 would be negative with respect to electrode 8. Foranodic polarity, the electrode 6 would have a voltage in the range of-100 to -1000 V while electrode 8 would have a polarity of -1 to -100 V,in which case, the polarity of the two electrodes would be such thatelectrode 8 would be negative with respect to electrode 6.

A pulse generator 12 is coupled by a lead 12A through a capacitor 12B tolead 8B and feedthrough 7. The pulse generator provides pulses ofvoltage which are additive to the voltage supplied by voltage source 8A.The pulses are applied to the electrode 8 for a purpose hereinafterdescribed. Control means 12AB is provided to vary each of the pulseheight, pulse width and pulse repetition rate of the pulses generated bypulse generator 12.

A lead 12C is directed through a feedthrough 9 and is coupled to thesubstrate 4 which places the substrate at ground potential.

A coil 11 is wound around housing 22 and is generally cylindrical suchthat a magnetic field generated by the coil when the coil is energizedwill be axial to the chamber 1. A means 11A is provided on the coil toenergize the same.

A second tubular coil 14 is provided to receive a coolant or heater forproviding temperature control of chamber 1. Means (not shown) isprovided to supply a coolant or heater to tube 14.

A viewing port 15 is provided to view the CVD process just above thesubstrate. Port 15 is also used in the measurement of pressure andresidual gas analysis in the chamber. The heater assembly 13 heats andcontrols the temperature of the substrate 4 outside chamber 1. Suchassembly 13 is not part of the vacuum system which is evacuating chamber1.

Chamber 1 has viewing port 17 through which a detector orspectrophotometer 18 can monitor the CVD process and can view the filmsurface of the substrate 4 through appropriate holes in the upper andlower electrodes 6 and 8. Port 17 also allows a light source 18, such asa scanning laser, to allow a photo-CVD (PHCVD) process to occur whenoptically transparent upper and lower perforated electrodes are used.

Chamber 1 has various ports such as inlet port 2 for reactants, exitport 3 for reaction products and pumping with a vacuum pump, and aload-locked entrance and retrieval port (not shown) for substrate 4, thesubstrate typically being a silicon wafer on which the chemical vapordeposition of films is to be accomplished. Chamber 1 can have a port foroptical viewing (not shown) of the inner structure in the CVD reaction.

Pulse generator 12 produces the desired electrical pulses which causethe final dissociation of the reactants between the lower electrode 8and substrate 4.

A typical CVD process is accomplished with apparatus 20 as follows:

1. A desired substrate 4 is introduced into the lower part of theapparatus 20 from the load-locked chamber through the entrance,retrieval port (not shown) on the substrate holder 10. Such a retrievalport is typically formed in a side wall of housing 22. The substrate ispositioned automatically by mounting means 16 which typically are pins.The chamber 1 is then evacuated to a desired base pressure, such as 1mTorr.

2. Heater 13 is energized to raise the substrate temperature to adesired value, such as 300° C.

3. Appropriate voltages are applied to upper and lower electrodes 6 and8. The polarities of the voltages (V₁ and V₂ of electrodes 6 and 8,respectively, and those of the electrical pulses from pulse generator 12depend upon desired dissociation characteristics of the reactants,whether or not they are cathodic or anodic. Examples of the voltageranges and polarities of the molecules of the reactants to be passedthrough the electric field are given as follows:

    ______________________________________                                        Cathodic       Polarity Anodic      Polarity                                  ______________________________________                                        V1    +100 to 100 V                                                                              -        -100 to 1000 V                                                                          +                                       V2     +1 to 100 V +          -1 to 100 V                                                                           -                                       ______________________________________                                    

4. The desired CVD reactants are then introduced into chamber 1 up to anappropriate pressure, such as 100 mTorr, such reactants being O3 orsilane.

5. Electrical pulses are appropriately applied by pulse generator 12 tothe lower electrode 8. Examples of the pulse height and polarities forthe cathodic and anodic cases are given as follows:

    ______________________________________                                        Cathodic      Polarity Anodic       Polarity                                  ______________________________________                                        V1   +100 to 100 V                                                                              -        -100 to 1000 V                                                                           +                                       V2   +1 to 100 V  +         -1 to 100 V                                                                             -                                       PG   -1 to 100 V  -         +1 to 100 V                                                                             +                                                         +                   -                                       ______________________________________                                    

6. The electrical pulses from pulse generator 12 are maintained for atime needed, such as 1 minute, for a desired film thickness, forinstance, 5000 Å. The characteristics of the pulses, for example, pulseheight, duty cycle, repetition rate, determine the properties of theprocess and films, for instance, blanket versus selective deposition,rate of deposition, stoichiometry, stress, grain size,anisotropy/isotropy.

7. The voltages are removed from electrodes 6 and 8 and pulse generator12 is shut down along with heater 13 and the flow of reactants intoinlet 2. The chamber 1 and space 24 are pumped down to a desired lowpressure, such as 1 mTorr in chamber 1.

8. The chamber 1 is back-filled with an inert gas, such as nitrogen. Thesubstrate 4 is removed through the load-locked chamber and the foregoingsteps are repeated for the next substrate.

In several CVD processes, for example, deposition of a metal such astungsten, in-situ cleaning and treatment of the surfaces in thecontacts, vias and trenches is quite important. Such in-situ cleaningand treatment processes are not easy, if not impossible, to accomplishwith currently available equipment. However, with the apparatusdescribed in the present invention, such in-situ cleaning and treatmentcan be accomplished and controlled easily as follows.

Before introducing reactants, appropriate in-situ cleaning reactants,such as H2 and CF4, are introduced, following which steps 5, 6 and 7 areperformed with the desired voltages on the electrodes 6 and 8, the pulsevoltage of generator 12 and time for both appropriate cleaning andtreatment of the surfaces. The anisotropy/isotropy of the cleaning canbe controlled by the process conditions, including chamber pressure. Forcontinuing with a CVD process, following the above in-situ cleaning andtreatment process, proceed from step 2 to step 8.

Typical In-Situ Etching After CVD of a Film for Planarization

In several CVD processes, e.g., deposition of SiO2 or W, in-situ etchingis required for the planarization of SiO2 or W-plug formation incontacts and vias. Such in-situ etching is possible in some conventionalequipment available currently, but the anisotropy and isotropy of theetching cannot be controlled easily; also, considerable radiation damageis introduced due to the unwanted electrons and ions generated in theplasma. However, with the apparatus of the present invention, suchin-situ etching with controlled anisotropy and isotropy can be doneeasily as follows, the radiation damage due to the electrons and ionsbeing small, if not non-existent, because high-density plasma is notgenerated by apparatus 20 of the present invention.

First, perform the steps 1 through 7 to complete the CVD process todeposit a desired film. Next, return to step 2 to start the in-situ etchprocess. After setting the temperature, V1 and V2 to the desired values,introduce appropriate etching reactants in step 4, such as CF4, SF6,CC14, CC12F2 or NF3, instead of the CVD reactants. Perform thesubsequent steps through step 8 to complete the in-situ etching afterCVD of a film.

Typical In-Situ Cleaning, Multi-Step, Multi-Chemistry CVD with In-SituEtching

For certain applications in microelectronics manufacturing, multilayersof dielectric and metal films are required. As an example, planarizedSiO2 layer capped with a Si3N4 layer is used in several applications.Such a planarized dielectric layer is not easy, if not impossible, todeposit with the conventional CVD equipment. However, with the presentinvention, such a layer can be deposited easily. A desired sequencing ofthe steps given above with appropriate reactants and process conditionswill produce such a layer.

Scaling Up the Size and Modification of the Electrode Shapes in ThisInvention for CVD/Etching/treatment on Non-Planar Surfaces, Such asHelicopter Rotor Blades, Turbines, Airplane Wings, and Space ShuttleNose Cones

For making the surfaces of various parts used in defense, space andindustrial applications more resistant to erosion and deteriorationunder hostile environments, it is helpful to coat the surfaces of theseparts with thin layers of suitable materials, such as Ti, Pt, SiC, Si3N4and Cr. No commercially available equipment can provide such coatingseasily. With the present invention, such coatings can be depositedeasily, uniformly and reproducibly. Apparatus 20 can be scaled up to thedesired size of the substrate to be coated.

Another key aspect of the present invention for such applications isthat the electrodes 6 and 8 can be shaped to conform to the non-planarsubstrate to be coated. By choosing appropriate reactants for CVD,etching and/or treatment, a desired film can be grown uniformly on thesubstrate whose shape can be non-planar or any surface contour. Byadjusting the voltages on electrodes 6 and 8, and the pulse height fromthe pulse generator, the deposition can approach surface implantationconditions and/or CVD of the desired film. Present techniques ofsputtering, evaporation and ion implantation cannot accomplish suchtasks easily or adequately.

What is claimed is:
 1. Apparatus for chemical vapor deposition of a filmon a substrate comprising:means defining a process chamber having agaseous inlet for receiving reactants and an outlet for gaseous flow outof the chamber; means in the chamber for mounting a substrate on which afilm is to be deposited; and means in the chamber for forming anelectric field between the inlet and said substrate mounting means forpolarizing the reactants, said electric field means including means forapplying a voltage pulse of sufficient magnitude to break the chemicalbonds of the polarized reactants to produce free radicals and ions whilekeeping the chamber free of plasma for use in depositing the film on thesubstrate.
 2. Apparatus as set forth in claim 1, wherein said electricfield means includes a pair of spaced electrodes in the chamber acrossthe path of the reactants flowing between the inlet and the outlet. 3.Apparatus as set forth in claim 1, wherein the electric field meansincludes a first electrode in the chamber, means for supplying a voltageto the first electrode, a second electrode in the chamber and spacedfrom the first electrode, a second electrical voltage source coupledwith the second electrode, said pulse generating means including a pulsegenerator coupled with one of the electrodes, and means coupled with thepulse generator for controlling the pulse height, duty cycle andrepetition rate of the pulses.
 4. An apparatus as set forth in claim 3,wherein the pulse generator is coupled to the second electrode, andwherein is included an electrical lead coupling the pulse generator withthe substrate.
 5. Apparatus as set forth in claim 1, wherein is includeda coil surrounding the chamber and having means for forming a magneticfield in the chamber.
 6. Apparatus as set forth in claim 5, wherein saidmagnetic field is axial with respect to the electric field.
 7. Apparatusas set forth in claim 1, wherein is included coolant flow or heatermeans surrounding the chamber for directing a coolant therethrough orheat for controlling the temperature of the chamber.
 8. Apparatus as setforth in claim 1, wherein is included the means below the substratemounting means for heating a substrate mounted in the chamber.